It is well known that color images are formed by oxidizing an aromatic primary amine color developing agent using exposed silver halide as an oxidizing agent, and making the oxidized color developing agent react with couplers.
Most of the magenta color-forming couplers which have been widely used in practice and which have received further study are 5-pyrazolone couplers. However, it is also known that the dyes formed from 5-pyrazolone couplers have an undesirable absorption in the vicinity of 430 nm, or a yellow component, which is responsible for turbidity in the developed color.
Magenta color image forming nuclei which can reduce the yellow component described above include pyrazolobenzimidazole nuclei as disclosed in British Patent 1,047,612, indazolone nuclei as disclosed in U.S. Pat. No. 3,770,447, pyrazolo(5,1-c)(1,2,4)triazole nuclei as disclosed in U.S. Pat. No. 3,725,067, pyrazolo(1,5-b)(1,2,4)triazole nuclei as disclosed in JP-A-59-171956 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") and U.S. Pat. No. 4,540,654, and imidazo(1,2-b)pyrazole nuclei as disclosed in JP-A-59-162548 and U.S. Pat. No. 4,500,630.
Magenta couplers having in particular pyrazolo(1,5-b)(1,2,4)triazole nuclei are known to be superior with respect to light fastness of the color images produced therefrom, so they are favorable for use in color photographic paper, compared with magenta couplers having other nuclei. In order to bring couplers into practical use, however, the couplers must satisfy many other properties (e.g., hue inside of the film, color formability), in addition to the fastness of the color images produced. Therefore, various efforts for improvements have been made, and a large number of proposals on improvements thereto have been submitted. Examples of improvements to couplers include a method of adopting an aryloxy eliminating type (JP-A-61 53644), a method of introducing an alkoxy or an aryloxy group at the 6-position of a pyrazolotriazole nucleus (JP-A-62-209457), a method of introducing a phenylene group at the 2-position of said nucleus (JP-A-63-41851), and a method of designing a ballast group to be introduced (JP-A-61-065246, JP-A-61-147254, JP-A-62-89961, JP-A-62-125349). However, these methods are still insufficient to allow the general utilization of the above-described type magenta couplers in color photographic paper because the couplers proposed entail a high production cost, the couplers are not sufficiently stable, or the couplers have unsatisfactory hue.